Method and system for detecting a property of a pavement by measuring gamma-radiaton

ABSTRACT

For detecting a property of at least one layer ( 301 ) of a pavement ( 300 ), a flux of radiation of energy levels or at least one range selected from an energy spectrum received from the pavement is measured in a position above the pavement. The measured radiation includes g-radiation emitted by at least one radionuclide in or under the pavement. Information regarding the property is determined from the measured flux and a relationship between at least one flux of g-radiation of the energy levels or the range or ranges selected from the energy spectrum and the property. Pavement layers typically contain different concentrations of g-radiation emitting radio nuclides than the roadbed or the soil underneath and this also applies to layers of pavement of different material compositions. Selectively processing measured radiation at different energy levels or in at least one selected energy range allows to determine information regarding properties of the pavement from measured g-radiation intensity more accurately.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a method for detecting a property of at leastone layer of a pavement, to a system for carrying out such a method andto a computer program for use in such a method.

It is known from practice, to measure physical parameters of a pavementwith ground radar. In this known method, radar waves are emitted by aradar source. The radar waves are partially reflected by the pavementand detected. The properties of the reflected radar waves may then berelated to physical parameters of the pavement. For example, theintensity or the phase delay of the reflected radar waves is a measurefor the thickness of the pavement.

However, a disadvantage of this known method is its complexity because aradar source and detector are required. Furthermore, it is difficult toidentify a boundary between layers having approximately the same densityand the emission and detection of radar waves may interfere with and beinterfered by other applications involving the use of radar signals,such as navigation and traffic control.

From Soviet patent application 1 617 078 it is known to measure theintensity of γ-radiation before and after the application of a dressinglayer and to use the difference between the measured total gamma rayintensities to assess the quality of the layer. However, the accuracy ofsuch measurements is quite unreliable.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a reliable solution fornon-destructive determination of a property of at least one layer of apavement.

According to the present invention, this object is achieved by carryingout a method for detecting a property of at least one layer of apavement in accordance with claim 1. Also according to the invention, asystem according to claim 10 for carrying out such a method as well as acomputer system according to claim 11 and a computer program accordingto claim 12 for processing radiation measurement data in such a methodare provided.

The measurement is reliable because it is hardly influenced by externalinfluences. By specifically measuring and processing γ-radiation ofvarious energy levels or at least one energy range, a more reliable andaccurate determination of the property to be determined can be achieved,because the γ-radiation can be processed in accordance with energylevels and ranges tailored to the γ-radiation spectra and differencesbetween γ-radiation spectra of the compounds of the pavement layer orlayers and of the road bed and the ground underneath as well as to theproperties to be monitored.

Specific embodiments of the invention are set forth in the dependentclaims.

Further features, effects and details of the invention are describedbelow with reference to the figures in the attached drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow-chart of a method according to the invention,

FIG. 2 schematically shows a vehicle provided with a system according tothe invention,

FIG. 3 schematically shows a cross-sectional view of a pavement,

FIG. 4 schematically shows the radiation flux of the pavement of FIG. 3,and

FIG. 5 shows a block diagram of a system according to the invention.

DETAILED DESCRIPTION

In the example of a method according to the invention shown in FIG. 1,in step 101 a flux of γ-radiation received from a road surface ismeasured. The flux, which may also be expressed in terms of theintensity of the radiation or the amount of radiation received over aperiod of time, can be determined for radiation emitted by a singleradionuclide (for instance ⁴⁰K, ²³²Th, ²³⁸U or the products of theirradioactive decay) or for radiation emitted by several radionuclides.Which method is to be preferred depends on the composition of thepavement layer or layers and of the roadbed and on the property orproperties to be measured. In step 102, a property of the pavement isdetermined from the measured flux or fluxes and data on the relationbetween the measured flux or fluxes and the property to be determined.The data on the relationship between measured flux and the property ofthe pavement layer to be determined, such as the materials used in thepavement or the thickness of (layers in) the pavement are obtained froma data store 103, for instance a computerized record such as a database.The steps 101, 102, 103 are separate steps, which may be carried out, ina single integrated apparatus. It is also possible to first collectradiation measurement data and to subsequently process these data in aseparate data processor. Preferably, the radiation measurement data areassociated to positional data. For calibrating the measurement results,use can also be made of calibration measurement results obtained fromcalibration samples physically extracted from the pavement, whichcalibration measurement results are preferably also associated topositional data and matched to radiation measurement data associated tothe same positional data.

The γ-radiation received from the pavement can be composed ofγ-radiation emitted by radionuclides in the pavement, radionuclides inthe roadbed (and/or in the soil) underneath the pavement or both. Thus,emission of radiation to the pavement is not required.

In general, the concentrations of radio nuclides in a pavement layer aresubstantially different from the concentrations of radio nuclides inother layers which may include a layer or layers of the pavement, theroadbed and the soil under the pavement. Moreover, each layer absorbsγ-radiation and each layer located above another layer absorbsγ-radiation from the layer or layers underneath as well. The flux ofγ-radiation received from the pavement by the detector is determined bythe composition of the layers of the pavement, the roadbed and/or thesoil underneath the pavement, the thickness or mass per unit of surfaceof the layers and the positions in vertical sense of the layers relativeto each other.

More specifically, the thickness of a layer influences the flux ofγ-radiation in two opposite ways: the thicker the layer, the moreγ-radiation is emitted from the layer, but the more γ-radiationoriginating from layers underneath is extinguished. Depending on thecomposition of the pavement, γ-radiation contributions significant forthe determination of the thickness of at least the topmost layer can bedetected from as deep as 20 to 50 cm below the top surface of thepavement.

A pavement may consist of one or more distinguishable layers ofdifferent material compositions, each containing differentconcentrations of radionuclides. From detected γ-radiation whichincludes contributions from the radionuclides in a plurality of layersand which is also determined by extinction in the layers, the thicknessof several layers can be estimated by measurement at energy levels orenergy level ranges characteristic for a plurality of radionuclides.

In almost all earth materials, (small) amounts of natural radionuclidesare present, such as ⁴⁰K, ²³²Th, ²³⁸U and the products of theirradioactive decay. Some of these radionuclides emit electromagneticγ-rays. The concentration of the radionuclides depends on, inter alia,the type of material, the origin of the material and the treatment ofthe material. For example, sand has a two to five times lowerconcentration of Th and U than clay. Thus, the specific mixture of theradioactive decay products is unique for each material. Hence, thecomposition of the pavement may be determined by measuring the radiationfrom the pavement and comparing the measured radiation withpredetermined references or ‘fingerprints’ of the constituents of thepavement composition. The composition of the pavement may also bedetermined by comparing the measured radiation directly with referencedata for different compositions.

For detecting the γ-radiation, various types of detectors can be used.In one type of detector, the radiation to be detected is allowed to fallon a crystal, which generates a light flash in reaction. A single photonmay cause such a light flash. These light flashes may then be applied toa photo multiplier or photodiode which converts the light flashes intoelectrical pulses. The number of pulses per unit time is a measure forthe flux of the radiation while the height of each electrical pulse is ameasure for the energy of the photon incident on the crystal. Bycounting the number of pulses for a period (for instance one to tenseconds) and sorting them according to pulse height, an energy spectrumcan be composed, i.e. the number of photons recorded per unit time as afunction of their energy.

Such a spectrum will contain peaks or lines, which are respectivelycaused at least substantially by the radionuclides mentioned. A peak ora set of peaks can then be ascribed to a nuclide. In addition,contributions from other physical phenomena are present in the spectrum,such as for instance the Compton effect. Nevertheless, the shape of thespectrum (i.e. the positions of the peaks and the Compton continuum) ischaracteristic for a given detector-pavement layer combination.

The vehicle 200 shown in FIG. 2 is provided with a system according tothe invention, a position determining system 205 and may also beprovided with other sensors known per se, such as sensors 206 formeasuring unevenness of the road. The system comprises a γ-radiationdetector 210 for measuring radiation received from below. Preferably, aplurality of detectors 210 is used so that a road can be scannedsimultaneously along several scanning tracks laterally spaced from eachother. The detectors can be shielded so that each detector receivesγ-radiation from a limited range of directions only, for instance from apredetermined solid angle or from a predetermined detection window onthe pavement which moves along the track to be scanned. The positiondetermining system 205 and the detector 210 are communicativelyconnected to a computer system 220. As is shown in FIG. 5, the computersystem 220 includes a processor 221 arranged to determine the propertyto be determined from the measured radiation and the data on therelation between radiation and the property to be determined stored in amemory 222. More specifically, the processor 221 may for instance beprogrammed to build up a γ-radiation spectrum over a preset time. Thedata regarding the measured γ-radiation and other measurement resultsare stored in a memory 222 in association with the position data fromthe position determining system 205 for on-line and off-line analysis.In such analysis, radionuclide concentrations or contributions from oneor more radionuclides may first be calculated. It is also possible todirectly compare the spectra with predetermined spectra corresponding toknown pavement constructions. The computer also includes an interface224 in the form of a display for signalling the results, such as thevalue of the determined property, and/or the quality of the analysis tothe user.

As is shown in FIG. 5, according to the present example the detector 210comprises a scintillation detector 211, known per se. The detectorcomprises a crystal that generates light flashes when photons of theradiation hit the crystal. The light flashes are converted to electricalpulses by a photo multiplier unit 212. The amplitude of the electricalsignals is a measure for the energy of the γ-radiation that has hit thecrystal.

The electrical signal is transmitted to a computer unit 213 in which theelectric signal is digitized and subsequently aggregated in a digitaldata set representing a spectrum. Each time a preset time-interval haselapsed, the spectrum and associated positional data are stored in amemory 214 of the computer unit 213. According to the present example,the spectrum is subsequently analyzed in terms of radionuclidecontribution data by using full spectrum analysis. For further detailsregarding full spectrum analysis, reference is made to “Full-Spectrumanalysis of natural γ-ray spectra”; P. H. G. M. Hendriks, J. Limburg, R.J. de Meijer; Journal of Environmental Radioactivity 53 (2001), pages365-380. On a display, the values of the radionuclide contribution dataand positional data associated to the trajectory from which themeasurements have been taken are displayed.

According to the present example, the desired information on thecomposition of the pavement is obtained via off-line analysis. Theobtained radionuclide contribution data are transmitted to the computerunit 220 via data bus 217. In the computer 220, the radionuclidecontribution data are corrected for the pavement conditions (such ascomposition and thickness of layers underneath). The correctedradionuclide contribution data are then converted to pavement build-updata using an algorithm containing the radionuclide contributions of thecompositions constituting the pavement build-up. These concentrationshave been determined beforehand in a separate laboratory analysis andstored in a database 223 in the memory 222 and can be inputted viainterface 225. The stored radionuclide contributions may for instance beassociated with materials for example in accordance with concentrationsof K, U and Th and radioactive decay products of U and Th in thosematerials.

The radiation can also be used to determine the thickness of one or morelayers of the pavement. In FIGS. 3 and 4, a pavement 300 having a singlelayer 301 is shown. The layer 301, which may for instance includebituminous, concrete or gravel material or shells, lies on top of a bed302. The pavement layer 301 and the bed 302 each contain concentrationsof natural radionuclei that emit γ-radiation with energy E_(γ). Theconcentration of a particular radio nuclide in the pavement layer 301 isC₁. The concentration of that nuclide in the bed 302 is C₂. Thethickness z₀ of the top-layer is to be determined. The bed 302 has athickness beyond a depth from which significant amounts of γ-radiationare received and is therefore assumed to have a virtually infinitethickness.

Supposing an ideal situation in which the γ-radiation detector 201 isplaced on a homogenous semi-infinitely extending layer. The γ-radiationflux towards the detector due to radionuclides with concentration C₁ ina layer of thickness dz is N₁dz. Due to absorption of photons bymaterial with thickness z_(z) between the layer of thickness dz and thedetector, the detector will detect a flux N of photons, which is equalto:n _(dz) =N ₁ e ^(−μ) ¹ ^(ρ) ¹ ^(z) dz  (1)

In equation (1), μ represents the mass-attenuation coefficient and ρ₁the bulk density of the material the pavement layer 301 is made of. Forthe top-layer 301 with thickness z₀, the flux of γ-radiation from thetop-layer received by the detector in an ideal situation is:$\begin{matrix}{{N_{1}^{tot}\left( E_{\gamma} \right)} = {{\int_{0}^{\pi_{0}}{N_{1}{\mathbb{e}}^{{- \mu_{1}}\rho_{1}z}\quad{\mathbb{d}z}}} = {\frac{N_{1}}{\mu_{1}\rho_{1}}\left( {1 - {\mathbb{e}}^{{- \mu_{1}}\rho_{1}z_{0}}} \right)}}} & (2)\end{matrix}$

The radiation flux resulting from the concentration C₂ in theground-layer 302 at the transition between the top and ground layer isequal to: $\begin{matrix}{{N_{2}\left( E_{\gamma} \right)} = {{\int_{0}^{\infty}{N_{2}{\mathbb{e}}^{{- \mu_{2}}\rho_{2}z}\quad{\mathbb{d}z}}} = \frac{N_{2}}{\mu_{2}\rho_{2}}}} & (3)\end{matrix}$

The radiation from the ground-layer is partially absorbed by thetop-layer. The flux of radiation from the ground layer 302, whichreaches the detector, is therefore equal to: $\begin{matrix}{{N_{2}^{tot}\left( E_{\gamma} \right)} = {\frac{N_{2}}{\mu_{2}\rho_{2}}{\mathbb{e}}^{{- \mu_{2}}\rho_{2}z}}} & (4)\end{matrix}$

Thus, the flux of radiation reaching the detector is equal to theradiation from the top-layer and the ground layer minus the amount ofabsorbed radiation. Mathematically the flux N (Eγ) is equal to:$\begin{matrix}{{N\left( E_{\gamma} \right)} = {{{N_{1}^{tot}\left( E_{\gamma} \right)} + {N_{2}^{tot}\left( E_{\gamma} \right)}} = {\frac{N_{1}}{\mu_{1}\rho_{1}} + {\left( {\frac{N_{2}}{\mu_{2}\rho_{2}} - \frac{N_{1}}{\mu_{1}\rho_{1}}} \right){\mathbb{e}}^{{- \mu_{1}}\rho_{1}z_{0}}}}}} & (5)\end{matrix}$

In FIG. 4, the flux from a radio nuclide is depicted schematically for atop layer which has a higher concentration of that radio nuclide thanthe soil underneath. The flux as a function of the position in thedirection indicated with arrow X shows changes at the positions x₀ andx₁ due to changes in the thickness of the top layer as is depicted inFIG. 3 at positions x₀ and x₁. The change in the flux is notproportional to the change in the thickness due to absorption in thepavement layer 301 itself. Hence, as is depicted in FIG. 4, whenscanning with the detector over the pavement, at positions x_(0,1) theradiation flux changes. Thus, the thickness of the layer or changestherein may be determined. Application of a method according to theinvention to determine the thickness of one or more layers in thepavement is especially suited to determine small changes in thethickness with a relatively large precision because the measuredradiation is inversely proportional to the exponent of the thickness.

The accuracy of the determination of the thickness may be increased bydetermining the contributions of various radio nuclides. For example,the contributions of γ-radiation emitted by ⁴⁰K and the several energiesof the γ-radiation emitted by decay products of ²³²Th and of ²³⁸U may bedetermined. Since both the absolute concentration and the relativeconcentrations of these radioactive products differ per layer, thethickness z₀ may be derived from a multiple of independent calculations,which increases the accuracy. Determining the contributions of a numberof radio nuclides individually also allows to cancel out variations inγ-radiation from the various radio nuclides emitted by materialunderneath the top layer of which the thickness is to be determined, sothat an accurate determination of top layer thickness can be achievedwithout separate measurement before application of the top layer.

Changes in thickness may be distinguished from changes in composition.Changes in thickness of a layer lead to a reduction or an increase inthe flux at the various energy levels of the radionuclides proportionalwith the specific contributions from the respective radionuclides inthat layer. Changes in composition typically lead to other changes inthe flux at the various energy levels that are different form changesproportional with the specific contributions from the respectiveradionuclides in that layer.

The mass-attenuation coefficient μ is hardly dependent on the materialand varies gradually and in a known manner with the energy of theγ-radiation.

The precision of the layer thickness measurement may be increased byanalyzing the full spectrum or at least energy ranges thereof whichcontain photo peaks and associated Compton continua. In this way moreinformation provided by the photoelectric effect and the Compton effectis utilized.

As indicated in FIG. 4, changes in the thickness of the top layer causechanges in the intensities of the γ-radiation measured at or above thesurface of the pavement. In practice, pavements often consist of severallayers, each with a different set of radionuclide concentrations.However, from the principles set forth above, the skilled person willreadily be able to formulate adapted algorithms to analyze suchmulti-layered pavement structures.

According to particular elaboration of the invention, the scintillationcrystal is mounted on a car. The car is driven over a road and thescintillation crystal collects γ-radiation from a scanned pavement trackalong the road as the car drives. With a cycle time of for instancebetween one and five seconds, received γ-radiation is registered in theform of data representing contributions over the energy spectrum. At 72km/h, this means that the measured radiation resulting in a spectrum haseach time been obtained from a scanned track of 20-100 m. After a lengthof road has been scanned, the spectra can be compared to identify wherechanges in the total flux and changes in the relative intensities, i.e.in the shape of the spectra have occurred. Such changes indicate changesin the build-up of the pavement.

Based on the results of this analysis, positions along the road can beidentified where samples can be taken that are representative forsections of the road where successive spectra were substantiallyidentical. Furthermore, the results of such analysis can also be used toensure that calibration samples are taken from the pavement only, ormainly, from sections of the road from which significantly differentspectra have been obtained and particularly where the spectra indicatechanges in the composition of the pavement material or of the soilunderneath, so that an effective contribution to the accuracy of thedetermination of the property of a layer of the pavement being scannedis obtained from each sample of road pavement.

Thus, the relationship between at least one flux of γ-radiation emittedby the at least one radionuclide and the property of the pavement to bedetermined can also be established after the γ-radiation measurementshave been taken to avoid the need of taking a plurality of samples whereno significant changes in the build-up of the pavement are to be found.

In practice it is often only required to check along the length of afreshly paved road whether the thickness of the pavement meets agreedstandards. One can then establish reference levels of γ-radiationintensity for one or more energy ranges in the spectrum that areassociated to the required thickness of the pavement or pavement layerassuming constant compositions of the road bed and the pavementmaterials. If the radionuclide concentration responsible for radiationin a certain range of the energy spectrum is higher in the pavement thanin the road bed, a radiation intensity in that energy range below thereference level indicates a too thin pavement layer (and vice versa ifthe concentration of the radionuclide is higher in the road bed). Afterscanning of the level of γ-radiation along the length of the road,stretches of road where the measurement signal indicates a too thinpavement can easily be identified and, optionally, samples from thepavement can be taken selectively to verify the measurement result.

By separately determining the γ-radiation contributions orconcentrations from a number of radio nuclides simultaneously, it isalso verified whether the assumption of constant composition of thepavement compound or compounds and the material underneath is valid. Ifthe thickness values calculated from γ-radiation contributionsoriginating from different radionuclides differ from each other morethan an acceptable tolerance range, an indication is obtained that theassumption of constant composition of the pavement layer or layers andof the material underneath the pavement is not valid and a new relationbetween γ-radiation intensities and (required) pavement thickness has tobe established.

An example of an application in which the material-composition of thepavement is of interest by itself is when a pavement is to bedemolished. Dependent on the material-composition of the pavementdifferent demolition techniques may need to be applied, recycling of thepavement material may be possible or not and the cost of demolition maybe different. For instance, if in some sections of a road, the pavementcontains polyaromatic carbohydrates which causes the pavement to beunsuitable for recycling whereas other sections are free from suchmaterials, it is of interest for the planning of the demolition wherethe sections containing polycyclic aromatic hydrocarbon (PAH) arelocated. Such sections can be identified on the basis of γ-radiationreceived while scanning the road. Pavement sections containing differentmaterials can be identified directly on the basis of differences inγ-radiation emitted by the different materials to be identified orindirectly on the basis of differences in γ-radiation emitted by otherconstituents typical for the mixtures containing the materials to beidentified. For instance a mixture of bituminous material containing PAHand a filler, such as sand, chalk or furnace slag, can also beidentified on the basis of differences between γ-radiation emitted bythe fillers associated to different materials containing PAH and notcontaining PAH.

From the above examples it is apparent that the determination ofinformation regarding a property of the pavement may take various forms.The determination of a property may for instance consist of obtaining anestimate for a value of that property, such as an estimate of thethickness of one or more pavement layers. It may for instance beadvantageous to scan the pavement at a low velocity of about 0.5 m/s orlower for providing machine control feedback during road construction.The determination of a property may also consist of merely establishingwhether the value of the property is above or below a reference value.The determination of a property may further consist solely inidentifying changes in that property, i.e. in establishing whether thevalue for a property, such as the thickness or the composition, haschanged significantly compared with another section of the pavement bycomparing the γ-radiation received from a portion of the pavement withthe γ-radiation received from another portion of the pavement.

1. A method for detecting a property of at least one layer of apavement, including: measuring, in a position above said pavement, atleast one flux of radiation received from said pavement and energylevels or at least one range within an energy spectrum of saidradiation, said measured radiation including γ-radiation emitted by atleast one radio nuclide in or under said pavement; and determininginformation regarding said property from said at least one measured fluxand energy levels or at least one range within the energy spectrum ofsaid γ-radiation and predetermined reference data for providing arelationship between at least one flux of γ-radiation of predeterminedenergy levels or in at least one predetermined energy range and saidproperty.
 2. A method according to claim 1, wherein at least oneγ-radiation contribution or concentration of at least one individualradio nuclide is determined from said at least one measured flux andenergy levels or at least one range within an energy spectrum of saidγ-radiation and from said reference data.
 3. A method according to claim2, wherein the radio nuclide is from a group consisting of ⁴⁰K, ²³²Th,²³⁸U and decay products of these radionuclides.
 4. A method according toclaim 2, wherein γ-radiation contributions or concentrations of aplurality of individual radio nuclides are determined.
 5. A methodaccording to claim 2, wherein said at least one γ-radiation contributionor concentration is determined by analyzing the energy spectrum of saidmeasured γ-radiation, said reference data including at least onereference spectrum of a reference concentration of an individual radionuclide.
 6. A method according to claim 1, wherein said property is thethickness of said at least one layer.
 7. A method according to claim 6,wherein said thickness is determined from a difference between the atleast one measured flux and at least one reference value for said atleast one flux, said at least one reference value being associated to aparticular thickness.
 8. A method according to claim 1, wherein saidproperty is the composition of said at least one layer.
 9. A methodaccording to claim 1, wherein said information is determined byanalyzing the spectrum of said measured radiation and comparing saidspectrum with at least one reference spectrum for a pavement compound orconstituent.
 10. A system for detecting a property of a pavement, saidsystem comprising: a radiation detector for measuring, in a positionabove said pavement, at least one flux of radiation received from saidpavement and energy levels or at least one range within an energyspectrum of said radiation, said measured radiation includingγ-radiation emitted by at least one radio nuclide in or under saidpavement; a signal processing structure for receiving from said detectora signal representing said at least one measured flux and energy levelsor at least one energy range of said measured γ-radiation and fordetermining information regarding said property from said signal andpredetermined reference data for providing a relationship between atleast one flux of γ-radiation of predetermined energy levels or in atleast one predetermined energy range and said property; and an interfacefor outputting data representing said property.
 11. A computer systemcomprising: an interface for inputting data representing at least onemeasured flux of γ-radiation emitted by at least one radio nuclide in orunder a pavement and associated energy levels or at least one associatedrange within an energy spectrum of said radiation; a database containingreference data for providing a relationship between at least one flux ofγ-radiation of predetermined energy levels or in at least onepredetermined energy range and said property; instructions fordetermining information regarding said property from said reference datain said database and said inputted data; and an interface for outputtingdata representing said property.
 12. A computer program for use in amethod for detecting a property of at least one layer of a pavement,including: instructions for reading inputted data representing at leastone measured flux of γ-radiation emitted by at least one radio nuclidein or under a pavement and associated energy levels or at least oneassociated range within an energy spectrum of said radiation; a databasecontaining reference data for providing a relationship between at leastone flux of γ-radiation of predetermined energy levels or in at leastone predetermined energy range and a property of at least one layer of apavement from which said γ-radiation is received; and instructions fordetermining information regarding said property from said reference datain said database and said inputted data.
 13. A data carrier deviceincluding data representing a computer program according to claim 12.14. A method according to claim 3, wherein γ-radiation contributions orconcentrations of a plurality of individual radio nuclides aredetermined.
 15. A method according to claim 3, wherein said at least oneγ-radiation contribution or concentration is determined by analyzing theenergy spectrum of said measured γ-radiation, said reference dataincluding at least one reference spectrum of a reference concentrationof an individual radio nuclide.
 16. A method according to claim 4,wherein said at least one γ-radiation contribution or concentration isdetermined by analyzing the energy spectrum of said measuredγ-radiation, said reference data including at least one referencespectrum of a reference concentration of an individual radio nuclide.17. A method according to claim 8, wherein said composition isdetermined by analyzing the spectrum of said measured radiation andcomparing said spectrum with at least one reference spectrum for apavement compound or constituent.